This invention relates to a method for making a semiconductor device, and more particularly to an improved method for making on a single semiconductor chip a semiconductor device having bipolar transistors, CMOS transistors, MOS capacitors and resistors formed on a single-crystal silicon semiconductor substrate.
A semiconductor device having bipolar transistors and CMOS transistors on a single semiconductor substrate, is generally called a BiCMOS device. VLSI-class BiCMOS technology of a prior art is mainly suitable for use in high-integration and high-speed logic or memory devices because it has been primarily developed for such objects. The BiCMOS technology of prior art for high-performance memory and logic devices has been disclosed in ISSCC Digest of Technical Papers, page 212, February 1986 and in CICC Technical Digest, page 68, May 1986, respectively. In achieving high-performance digital and analog VLSI devices on a single chip with the prior art, there are often limits in the performance and application because there are not optimized and prepared therein for MOS elements, bipolar elements, resistors and capacitors to simultaneously perform precise analog functions and high-speed, high-integration digital functions. In the meanwhile, the influence that the interface between single-crystal emitter region and polycrystalline silicon in a polycrystalline silicon emitter bipolar transistor element has upon the characteristic of elements and circuits, has been disclosed in IEEE, ED-34 NO. 6, PP 1346-1353, June 1987 and in Symposium VLSI Technical Digest papers, PP 47-48, May 1986.